drm_hwcomposer: Check the composition before sending to frame worker

drm_hwcomposer: Check the composition before sending to frame worker

Before we send a composition to the frame worker and display, run it
through the kernel to test whether it can be put on hardware. If the
kernel rejects the composition, use the squashing code to flatten it
on one layer and send the result to the frame worker.

Bug: 25379136
Test: Tested on smaug, frames were squashed, fun was had

Change-Id: Icac3c034d0eb4c0becbdc0f8ace1de75ab8ae2b8
Signed-off-by: Sean Paul <seanpaul@chromium.org>